A few days later, Wonkroom’s Brad Johnson (a colleague of Romm’s at the Center for American Progress) shook things up when he published interviews with three eminent climatologists. The most assertive statements came from Kevin Trenberth, head of the Climate Analysis Section of the National Center for Atmospheric Research, and Michael Mann, director of the Earth System Science Center at Pennsylvania State University. They told him, respectively, that “It is irresponsible not to mention climate change. … The environment in which all of these storms and the tornadoes are occurring has changed from human influences (global warming),” and “Climate change is present in every single meteorological event, in that these events are occurring within a baseline atmospheric environment that has shifted in favor of more intense weather events.”
The third, and most complete, quote came from Gavin Schmidt, a climate modeler at the Goddard Institute for Space Studies, who said:
It is a truism to say that everything has been affected by climate change so far and therefore this latest outbreak must in some sense have been affected, but attribution is hard, and the further down the chain the causality is supposed to go, the harder this is. For heat waves it is easier, for statistics on precipitation intensity it is easier — there are multiple levels of good modeling, theory, and observations to back it up. But we have much less to go on with tornadoes.
Andrew Revkin put it a little more bluntly at his New York Times Dot Earth blog:
There’s no doubt that Michael Mann of Pennsylvania State University is right when he says “climate change is present in every single meteorological event” — in the sense that the buildup of greenhouses gases is a background nudge everywhere.
But that’s a meaningless assertion without asking whether there is evidence of a meaningful influence — meaning enough of a nudge to the atmosphere that the contribution from greenhouse gases is relevant to policy and personal choices, in this case in tornado zones.
Most major news outlets have done a good, stressing the immediate meteorological causes of the tornadoes and the high level of uncertainty surrounding their relation to climate change. Take the Q&A-style explainers published May 25 in the The New York Times and Los Angeles Times on pages sixteen and seventeen of the papers’ A sections, respectively. Take wire services like the Associated Press and Agence France-Presse, or magazines like Time. Take regional outlets like The Christian Science Monitor, the Houston Chronicle, the Kansas City Star, the Toledo Blade in Ohio, and the Anniston Star in Alabama. Take specialty publications like ClimateWire, LiveScience.com, and New Scientist.
One could pick nits with all of these pieces, but they faithfully and carefully convey the message of a preliminary report on April’s tornadoes from the National Oceanic and Atmospheric Administration’s (NOAA) Climate Attribution Rapid Response Team:
A change in the mean climate properties that are believed to be particularly relevant to major destructive tornado events has thus not been detected for April, at least during the last 30 years. So far, we have not been able to link any of the major causes of the tornado outbreak to global warming. Barring a detection of change, a claim of attribution (to human impacts) is thus problematic, although it does not exclude that a future change in such environmental conditions may occur as anthropogenic greenhouse gas forcing increases.
Some pieces didn’t display enough skepticism. A USA Today post, titled “Climate change could spawn more tornadoes,” is one example. It cited studies in Proceedings of the National Academy of Sciences and Geophysical Research Letters to support the headline’s assertion. Those papers focused on severe thunderstorms, which can create tornadoes and are likely to be more frequent in a warming world, but they didn’t actually say much about twisters themselves (which are not inevitable byproducts of severe thunderstorms).